The present invention relates to a method and diagnostic kit for detecting platelet antibodies specific for human leukocyte antigens (HLA) class I as well as antibodies specific for platelet surface glycoproteins. These antibodies occur in the human population with an incidence of 30% or less causing platelet dysfunction. Since platelet dysfunction can occur for reasons other than the presence of the stated antibodies, their detection is important for patient diagnoses.
Blood obtained from different individuals has been found to have different antigenic and immune properties, to the extent that antibodies in the blood of one person may react with antigens on red blood cells or platelets in the blood of another individual. These antigens are often found on membrane glycoproteins present on the surface of the cell membranes. The antigens are also found on HLA which are also associated with platelets.
The blood platelet is one of the four primary elements that are important in maintaining hemostasis. It is a single cell that uses both its contents and cellular functions during the coagulation process. Platelets release mediators which promote a number of responses that are capable of initiating the hemostatic mechanisms and functions. These mediators may recruit other platelets to form an aggregated mass of coagulated platelets.
Patients who have normal or borderline platelet counts and a long bleeding time usually have a problem with platelet dysfunction. As the interaction of the platelet with vascular wall is important in determining the length of the bleeding time, vascular abnormalities can also mask platelet dysfunction in rare instances. Both hereditary and acquired types of platelet dysfunction may be seen clinically.
An immunological destruction of platelets can occur in patients with select hematologic disorders such as leukemia, systemic lupus erythematosis or other collagen-vascular diseases, viral infections, or in patients who have experienced alloimmunization because of a pregnancy or a transfusion. Therefore, it is important for physicians to properly diagnose and choose appropriate therapies for patients with bleeding problems caused by platelet dysfunction.
The presence of antibodies in the human circulation directed against foreign HLA signifies a unique immune state, termed HLA alloimmunity. This condition usually develops after direct, often unintentional exposure to a dose of foreign HLA antigens. The most common situation leading to HLA alloimmunity is pregnancy, because childbirth frequently exposes the mother to paternal HLA antigens carried on fetal blood cells. However, in medicine, blood component transfusion therapy frequently causes alloimmunization. Among mukitransfused subjects, the incidence of HLA alloimmunity ranges between 30 and 70%. See Schiffer et al., Blood 58:1007-11 (1981).
Neonatal alloimmune thrombocytopenic purpura (NATP) and posttransfusion purpura (PTP) are syndromes resulting from sensitization to platelet-specific alloantigens complexing with platelet glycoproteins. Autoimmune thrombocytopenia (AITP) represents a frequent kind of immune thrombocytopenia. This disease also manifests itself in the production of autoantibodies to platelet glycoproteins.
The diagnosis of these diseases in the dinical setting is often difficult. This is primarily because many factors may contribute to platelet dysfunction. Often, the individuals are receiving intense cancer therapy, or they may have received bone marrow or solid organ transplants. They may be patients who have suffered severe trauma or have recently had major surgery. Each of these clinical conditions is frequently accompanied by complications that reduce the effectiveness of platelet transfusion therapy. When platelet dysfunction symptoms appear, clinical distinction is frequently difficult if not impossible. Therefore, laboratory investigation complementing clinical diagnosis is particularly helpful.